There may have been smaller campylobacter outbreaks in Hawke's Bay that were never picked up by health officials, researchers studying the 2016 Havelock North outbreak say.

That possibility is being investigated as part of a two-year study into the Havelock North water crisis, where 5000 people fell ill in August 2016.

Hawke's Bay has had one of the highest rates of campylobacter, per capita, in the country for several years and researchers were looking at historical trends between heavy rainfall and all types of reported gastroenteritis cases.

"The question is ... could it have happened without us even noticing?" Hawke's Bay District Health Board's population health acting director Dr Nicholas Jones said.

They're also collecting anecdotal information from pharmacists and Plunket nurses who were among the first to see cases of illness in 2016.

"Schools were saying that they'd had children off, but we in the public health unit had no idea about any of that," Dr Jones said.

Social media posts on Twitter and Google trends from around the time of the outbreak were also being analysed to see if it could have been detected sooner, he said.

The aim was to create early detection systems that prevent or lessen the severity of future outbreaks.

Another part of the study looking at long-term effects on those who did get sick would get underway in the next few months.

It was being led by Hawke's Bay District Health Board medical director and nephrologist (renal physician) Dr Colin Hutchison.

Long term, campylobacter patients could suffer inflammation conditions such as arthritis or organ damage, he said.

"This is the biggest outbreak in the Western world in many years ... it's a really unique opportunity to study the complications."

Meanwhile, Havelock North contamination was comparable to the the 2014 Flint Michigan water crisis, according to Massey University school of health sciences lecturer Stuart McLaren.

While not part of the formal study into the outbreak, he had carried out his own analysis of the crisis and its similarities with Flint.

"There are about four or five quite serious parallels which is quite extraordinary when you consider these two are quite different. Yet both government inquiries into these came up with these series of failures."

Dr McLaren hoped to publish his comparison of the two crises in a scientific journal soon.